1. Field of the Invention
The present invention relates to a mold in which a body member supports an insert member having a cavity surface via a plurality of balls.
2. Description of the Related Art
A mirror frame which is a member for supporting an optical system for a digital camera or a telescopic lens requires an extremely high level of processing accuracy because such a mirror frame has a great influence on accuracy of an optical axis in the optical system. In addition, the accuracy of an optical axis is especially important to the performance and quality of a product. For instance, when ten lenses are used for an optical system, it has been common to manufacture a mirror frame one of whose lenses is designed to be fine-adjustable and, by fine-adjusting the lens, the optical axis can be finally adjusted. A small-sized mirror frame manufactured by means of plastic injection molding has been widely used as a mirror frame for supporting an optical system for a film camera with a lens, a cellular phone with a built-in camera, or the like. Further, a lens itself, constituting an optical system, has been formed by means of plastic injection molding, and the accuracy of an optical axis is highly important also in manufacturing such a lens.
As a mold capable of manufacturing a product with high accuracy, for example, a mold 500, as shown in FIG. 3, has been known which has a cavity between a first half 600 and a second half 700, and a product is injection-molded in the cavity (See, for example, Japanese Published Patent Application No. 2003-231159, paragraphs 0020-0029, FIG. 1). The first half 600 comprises an insert member 610 having a cavity surface 610a; a body member 620 for holding the insert member 610 from outside and having a tapered protrusion 621 on an end face thereof on the side of the second half 700; and a ball retainer 630 for intervening between the insert member 610 and the body member 620. Further, the second half 700 comprises an insert member 710 having a cavity surface 710a; a body member 720 for holding the insert member 710 from outside and having a reversely tapered part 721 on an end face thereof on the side of the first half 600; and a ball retainer 730 for intervening between the insert member 710 and the body member 720.
In the mold described above, the intervention of the ball retainers 630, 730 enables the center axis alignment between the insert member 610 and the body member 620 and between the insert member 710 and the body member 720 respectively, and, in the meantime, the use of the tapered protrusion 621 and the reversely tapered part 721 enables the center axis alignment between the first half 600 and the second half 700. In such a mold, a molded product is removed when the insert member 610 is moved with respect to the body member 620.
In the mold described above, in the meantime, there is a possibility that a track surface of the mold deteriorates in a case where a material for the spherical members is harder than that for the mold (an insert member and a body member thereof), because the spherical members roll between the insert member and the ball retainer or between the ball retainer and the body member every time a molded product is removed. There is another problem that, when the track surface of the mold is ground off, the resultant ground matters further grind off the mold, and the ground matters or ground irregularities misalign the spherical members to degrade the center axis alignment of the insert member. It is to be noted that the problems described above tend to occur easily, because, in general, such a mold is made of brass, aluminum, copper, a stainless steel product (HRC 33-52) plated with nickel or copper, or the like in consideration of easier processing, while in turn, the spherical members are made of bearing steel (HCR 58-64) or the like, which is harder than the former. To solve such a problem, if the material for a mold is designed to be harder than that for the spherical members, there occurs a problem that a mold is difficult to be machined to thereby raise the production cost, or that a desired processing accuracy of a molded product cannot be obtained using a harder material for the mold.
There is also a problem that, because the material for the mold described above is not sufficient in stiffness against a pressure applied when a molten resin is filled into a cavity, the spherical members are pushed (sunk) into the mold to degrade accuracy in the center axis alignment between the insert member and the body member.
For the reasons described above, an object of the present invention is to provide a mold capable of preventing deterioration of the mold even when the material for the spherical members are harder than that for the mold, and capable of aligning the center axis between the insert member and the body member with high accuracy even when the pressure of resin filling is applied thereon.